A large number of pressure-operated control valves have been developed. In these types of valves, a pressurized fluid (water, air or other liquid or gas) selectively closes or opens a seal in the valve to regulate the flow of liquids or gases through the valve. Two examples of valves which belong to this large family include diaphragm valves (in which a pressurized fluid selectively forces a diaphragm against a valve seat to shut off the flow of a liquid) and globe valves (which have a somewhat globe-shaped housing including a control chamber in which a fluid pressure controls passage of a liquid through the control chamber).
A problem which challenges design of prior art pressure-operated control valves is attaining good flow characteristics, i.e., minimizing pressure drop and turbulence through the valve.